Dependencies: Tfvars

As mentioned in Deploy Multiple, Terraspace allows you to deploy multiple stacks with a single command. Terraspace automatically detects the dependencies when you wire the outputs of one stack to another stack’s input variables.

Here is some additional info about the dependencies-related helper methods.

Name Description
output Wire stack outputs to inputs. Terraspace will infer the dependency.
depends_on Explicitly configure the dependency.

output helper

The general form for output is

output("DEPENDANT_STACK.OUTPUT_KEY", options={})

Where DEPENDANT_STACK is another stack in your terraform project, and OUTPUT_KEY is an output defined in that stack. Here’s an tfvars example:

app/stacks/instance/tfvars/base.tfvars

vpc_id = <%= output('vpc.vpc_id') %>

Mock Values

When running terraspace plan all, the dependent stacks may not have been applied yet. You can provide mock values so the plan can be successful. Example:

app/stacks/instance/tfvars/base.tfvars

vpc_id = <%= output('vpc.vpc_id', mock: 'vpc-111') %>

The mock values are only used if the dependent stacks have not yet been applied. Once the dependent stacks are applied, actual values are used instead.

depends_on helper

There is also a depends_on helper method that can be used to declare dependencies without having to wire outputs to input variables. Example:

app/stacks/instance/tfvars/base.tfvars

<% depends_on('vpc') %>

Remember you do not need to declare depends_on if you are already using output to inputs to outputs. Terraspace will infer the dependencies automatically. It is fine to declare both, though you may forget to remove the depends_on declaration when you remove all the output declarations.

You can also specify multiple stacks with depends_on:

<% depends_on('vpc', 'redis', 'mysql') %>